The headline’s true, but a bit sensational. However, it’s from a recent paper that has attracted a lot of attention: Being licked by a dog can be fatal: Capnocytophaga canimorsus sepsis with purpura fulminans in an immunocompetent man (Mader et al. 2019).

This recent fatal Capnocytophaga canimorsus infection in a German man has gotten a lot of attention. It’s a bit of an obscure bacterium, despite being present in the mouth of pretty much every dog, and one that I disproportionately talk about a lot because it’s not well known but has the potential to cause very serious disease in people. Most veterinary professionals don’t have much background on C. canimorsus, since it doesn’t typically cause disease in animals.  However, it’s important to know about it when talking to dog owners about risks from bites. When I talk to physicians, there’s usually a similar lack of recognition.

While this bug is common in dogs, human infections are rare. They usually occur in people without a functional spleen or in people who have compromised immune systems. In those individuals, a bite or other type of contact with dog saliva in wounds/broken skin or on mucous membranes (e.g. mouth, nose, eyes) creates the potential for infection, and is an indication for prophylactic antibiotics.

In the general population, infections are exceptionally rare, which is why this particular case report is so unique.  It describes a fatal infection in a 63-year-old man who was otherwise healthy and had no known immunocompromise.

  • That’s really rare.

He had a dog and had not been bitten, but had been licked.

  • That’s rare too as far as risk for infection with this bacterium, but it happens.

He developed severely progressive disease and ultimately died after 16 days of aggressive care.

  • Unfortunately, that’s not rare. A large percentage of infected people die, and those who survive often have devastating complications, including loss of digits or limbs.

The authors drew a couple of conclusions:

Pet owners with flu-like symptoms should urgently seek medical advice when their symptoms exceed those of a simple viral infection, which in this case were severe dyspnoea and petechiae. Physicians confronted with such patients should ask about contact with dogs and cats.

  • I’d expand that to contact with any animal, since this bacterium is not the only issue. Furthermore, everyone plays a role here. Patients and their families should report animal contact if  their healthcare provider doesn’t ask.

They [healthcare providers] should consider C. canimorsus infections also in the presence of purpura fulminans and the absence of animal bites or scratches, and any immunodeficiency. In such cases, the clinician should immediately start empiric treatment with a penicillin in combination with a beta-lactam inhibitor until a definite diagnosis is established.

  • It’s hard to say that Capno should be considered in every person. I guess it’s fine to say “think about it,” but common things occur commonly, and this infection in a healthy person isn’t one of them. Early recognition is important and fortunately, someone coming with this severe of an infection would be expected to be immediately started on an antibiotic  anyway that would also kill Capno (since it’s susceptible to a range of antibiotics).

For me, the key is preventing things from getting to this stage in the first place through common sense measures to decrease risk in high-risk individuals, and early recognition of a combination of risk factors. That doesn’t apply to an odd case like this, but it does to the majority of cases where there’s known (but not necessarily recognized) immunosupression of the patient, lack of recognition of the potential problems from a dog bite, and frequent lack of communication about animal exposure and bites. Failure to realize the risk in high-risk persons contributes to many deaths.

More information about Capnocytophaga canimorsus can be found in the fact sheet on the Worms & Germs Resources – Pets page.